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Combining Rogers 4003C and FR4 in layer stackup

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Hi all,
We are trying to make a 4-layer PCB for 5.8 GHz power amplifier application. The circuit has been verified on a two layer board, but to take care of better connectorization, we are going for 4 layer board.
Here we want to have the following stackup:
+ Top layer and Mid layer1 from RO4003C 20 mil PCB
+ Mid layer2 and Bottom layer from FR4 20 mil PCB
+ Prepreg layer of FR4 of thickness 20 mil in-between the two PCBs.

The problem is that FR4 and RO4003C have very different Tg (glass transition temperature); FR4 has Tg of 150 degC and RO4003C 280 degC. Will this result in any board reliability issue during manufacturing or during operation? Any help on this is most welcome.

Thanks in advance.
 

I would expect serious warping due to the asymmetrical stackup. If lamination of FR4 and 4003C works at all, it should use a symmetrical layer sequence. What's your PCB manufacturer's opinion about the design? Possibly you should also contact Rogers. I have experienced, that a major PCB manufacturer made a Rogers/FR4 hybrid design (a different substrate than 4003) which finally failed. Then Rogers was asked about the combination, and they said, it could never work...
 

Hi FvM,
Thanks for the quick reply. What material would you suggest that would make a great combination with RO4003C? We have already put this question to Rogers. I think if we take care of the thermal expansion coefficients of the hybrid materials to be similar, there shouldn't be an issue.
 

I have no suggestions. In the said case, 3203 had been used, but the multilayer delaminated during reflow processing.

I fear, thermal expansion will never match exactly, the different Tg you mentioned is one reaon for it. Thus I have doubts at leat for the assymetrical stackup. Of course, the significance of possible warping issues depends on the board size and other paramters.
 

Hi FvM,
Just got a reply from Rogers. They have guaranteed that there would be no issue during reflow processing as this is usually done for a couple of minutes.
Thanks for the help.
 

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